Network-assisted direct device-to-device (D2D) communication is expected to be a key feature supported by next generation cellular communication networks. FIG. 1 illustrates a cellular communication network 10 that enables direct D2D communications. As illustrated, the cellular communication network 10 includes a base station 12 that serves a corresponding cell 14 of the cellular communication network 10. While only one base station 12 is illustrated, the cellular communication network 10 includes numerous base stations 12 serving corresponding cells 14. In this example, wireless devices (WDs) 16, 18, 20, and 22 are located within the cell 14. The wireless devices 16 and 18 are in proximity to one another. As such, when the wireless devices 16 and 18 desire to establish a bearer link, rather than establishing the bearer link through the base station 12, the cellular communication network 10 assists the wireless devices 16 and 18 to establish a direct D2D communication link (i.e., a direct D2D bearer link) between one another. More specifically, through signaling with the base station 12 or some other mechanism, the wireless devices 16 and 18 discover one another using a D2D device discovery process and then establish a D2D communication link directly between one another rather than through the base station 12.
Direct D2D communication is possible regardless of whether the cellular communication network 10 is Frequency Division Duplex (FDD) (i.e., uses different uplink and downlink frequency bands) or Time Division Duplex (TDD) (i.e., uses the same frequency band but different time slots for uplink and downlink). However, it is commonly accepted that direct D2D communication links, such as that established between the wireless devices 16 and 18, is preferably a TDD communication link where transmission by one wireless device uses the same resources as reception by the other wireless device. These “resources” are physical frequency and/or time resources depending on the particular implementation of the cellular communication network 10. TDD (i.e., half duplex operation) is preferred because operating a transmitter and a receiver in the same frequency band in a half duplex fashion is easier to implement than a full duplex FDD implementation.
In order to provide spectral efficiency, it is preferable for the D2D communication link to use the same resources as those used by the cellular communication network 10 where the cellular communication network 10 performs actions such as mode selection, network-controlled scheduling, and power control. In this example, the D2D communication link uses either an uplink resource or a downlink resource of the cellular communication network 10. The same uplink resource or downlink resource is, or at least can be, also used for the uplink from or downlink to another wireless device in the cell 14 such as, for example, the wireless device 22. Likewise, the same uplink resource or downlink resource is, or at least can be, also used for the uplink from or downlink to other wireless devices in neighboring cells. As such, while using the same resources as the cellular communication network 10 provides spectral efficiency, doing so also gives rise to new intra-cell and inter-cell interference situations. For example, due to the presence of D2D communication links, intra-cell orthogonality is no longer maintained.
Specifically, when the D2D communication link between the wireless devices 16 and 18 uses a downlink (DL) resource of the cellular communication network 10 and the same DL resource is also used by the wireless device 22, strong intra-cell interference may be caused for the wireless device 22, as illustrated in FIG. 2. For simplicity and for the clarity of presentation, the case of intra-cell DL interference is displayed in FIG. 2. The case of inter-cell, or other cell, interference resulting from the direct D2D communication link between the wireless devices 16 and 18 can be easily deduced. The transmission from, for instance, the wireless device 16 over the D2D communication link to the wireless device 18 using the DL resource of the cellular communication network 10 may result in interference to a wireless device located in a neighboring cell that uses the same DL resource. It should also be noted that transmissions by the wireless devices 16 and 18 over the direct D2D communication link result in interference to other nearby wireless devices (not shown) regardless of whether those other wireless devices use the same DL resource (e.g., the same resource blocks in an Orthogonal Frequency Division Multiplexing (OFDM) downlink frequency band).
Similarly, when the D2D communication link between the wireless devices 16 and 18 uses an uplink (UL) resource of the cellular communication network 10 and the same UL resource is also used by the wireless device 22, strong intra-cell interference may be caused to the base station 12 serving the cell 14 for the uplink from the wireless device 22, as illustrated in FIG. 3. For instance, transmission by the wireless device 16 over the D2D communication link to the wireless device 18 using an uplink frequency band of the cellular communication network 10 may result in interference to the base station 12 for an uplink from the wireless device 22 using the same uplink frequency band. As with the downlink interference, the case of inter-cell interference resulting from D2D communication using UL resources can easily be deduced. Transmissions from, for example, the wireless device 16 over the D2D communication link to the wireless device 18 using the UL resource may also generate interference to base stations serving neighboring cells for uplinks from wireless devices in the neighboring cells that use the same UL resource. Notably, the base stations that serve the neighboring cells are referred to herein as neighboring base stations. It should also be noted that transmissions by the wireless devices 16 and 18 over the direct D2D communication link using the UL resource result in interference to the base station 12 regardless of whether other wireless devices (not shown) use the same UL resource (e.g., the same resource blocks in an OFDM uplink frequency band).
From the discussion above, it is readily understood that D2D communication using the same resources used for downlinks and uplinks in the cellular communication network 10 results in new interference scenarios not envisioned in conventional cellular communication networks. Further compounding the issue is the fact that the cellular communication network 10 may have both conventional base stations (e.g., eNBs in a Long Term Evolution (LTE) network) and low-power base stations (e.g., pico base stations, Closed Subscriber Group (CSG) Home eNBs, and/or relays in an LTE network). In such a heterogeneous network, D2D communication using the same resources used for downlinks and uplinks in the heterogeneous network result in even more new interference scenarios not envisioned in conventional cellular communication networks. As such, there is a need for systems and methods for minimizing, or at least substantially reducing, interference resulting from D2D communication in a cellular communication network and, in particular, a heterogeneous cellular communication network.